In this report, three problems of hull deflection during construction will be dealt with. First the deflection of that part of the vessel's bottom which overhangs port & starboard of the concrete building berth will be discussed. Secondly the deformation of superstructure decks during the completion of work after launching will be discussed. The third and major topic of discussion will be the problem of the deformation of the vessel's bottom and inner bottom in way of machinery room in connection with the problem of propeller shaft centerline alignment and/or boss boring. In regard to this problem, the following findings will be shown : (1) The rate of rising of the stern is greatest during the earlier period of construction and decreases gradually as the work progresses. The amount of eccentricity of stern tube bossing when ploted against progress of work gives the “Sine” curve. (2) The athwartship deflection of the vessel's stern either to port or starboard is strongly influenced by seasonal, climatic conditions. (3) The fore & aft shrinkage of the stern part of vessel's hull is greatest during early stages of construction (as is the case of the stern rising). The rate of shrinkage of the main deck does not necessarily coincide that of the vessel's bottom. Finally, the shrinking force resulting from welding and heating will be discussed together with the result of some experimental model tests to confirm the fact that the fore & aft shrinkage of the vessel is caused to far greater degree by the welding on the ship's bottom and its vicinity than the welding on the main deck and above.